A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a user drives a car having a vehicle navigation system. Such a navigation system detects the position of the user or user's vehicle, reads out map data pertaining to an, area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Alternatively, such map data can be provided to the user from a remote server through a communication network such as Internet. The navigation system displays a map image on a monitor screen while superimposing a mark representing the current location of the user on the map image.
When a destination is set, the navigation system starts a route guidance function for setting a guided route from the start point to the destination. To determine the guided route to the destination, the navigation system calculates and determines an optimum route to the destination based on various parameters. For example, the guided route is determined based on the shortest way to reach the destination, the route preferring freeways to surface roads, the least expensive way to the destination, or the route without using toll road, and the like.
During the route guidance, the navigation system reads the nodes data from the data storage medium such as DVD and successively stores the nodes data of road segments (expressed in longitude and latitude) constituting the guided route in a memory. In the actual traveling, the node series stored in the memory is searched for a portion of the guided route to be displayed in a map display area of the monitor, screen, and the portion of the guided route is highlighted so as to be discriminable from other routes. When the vehicle is within a predetermined distance of an intersection it is approaching, an intersection guidance diagram (an enlarged or highlighted intersection diagram with an arrow indicating the direction in which the vehicle is to turn at the intersection) is displayed to inform a user of the desired one of roads or directions selectable at the intersection. Such route guidance by the navigation system is also given by voice instruction.
FIGS. 1A-1H show an example of overall procedure and screen display involved in the navigation system. FIG. 1A shows an example of locator map screen of the navigation system when the destination is not specified. Typically, the navigation system displays a street on which the vehicle (current vehicle position VP) is running on a map image and a name of the street. Other information such as a north pointer NP, a map scale and a current time may also be illustrated on the display screen. However, in this, situation, the navigation system does not perform the route guidance function because the destination is not specified.
FIGS. 1B-1F show an example of process for specifying a destination in the navigation system. When selecting a “Destination” menu on a main menu screen (not shown), the navigation system displays an “Find Destination By” screen as shown in FIG. 1B for specifying an input method for selecting the destination. The “Find Destination By” screen lists various methods for selecting the destination. The methods include “Address” for specifying the city and address of the destination, “Intersection” for specifying the names of two streets which intersect with one another, and “Point of Interest” (POI) for selecting the programmed destination based on the name, category or telephone number. Other methods in the “Find Destination By” screen include “Recent Route” for specifying the destination based on the recent history of destinations saved in the navigation system, “Address Book” for selecting the address of the destination out of the prescribed address list stored in the system, and “Today's Plan” for selecting two or more destinations.
When selecting, for example, the “Point of Interest” method in FIG. 1B, the navigation system displays selection methods of point of interest (POI) either by “Place Name” or “Place Type” in FIG. 1C. The “Place Name” is to specify a name of POI, and the “Place Type” is to specify a category of POI. If the “Place Type” is selected in FIG. 1C, the navigation system shows an “Select Category” screen such as shown in FIG. 1D. The screen of FIG. 1D lists categories of POI such as “ATM”, “BanK”, “Gas Station”, “Hospital”, “Movie Theater”, and “Restaurant”.
Suppose the user selects “Restaurant”, the navigation system retrieves the POIs in the selected category, restaurant, in this case, as shown in FIG. 1E. Typically, POIs (restaurants) will be listed in the order of distance from the user (ex. current vehicle position). If the user selects a particular restaurant from the list, such as “Genkai”, the navigation system displays a “Confirm Route” screen such as shown in FIG. 1F. In this example, the “Confirm Route” screen lists the name, address and phone number of the destination (POI specified by the user). If this is the correct destination, the user enters an “OK to Proceed” key to proceed to the next procedure.
In FIG. 1G, the navigation system calculates and determines a route to the destination, i.e., the selected POI. The navigation system determines a route to the destination based on, for example, the shortest way to reach the destination, the route using many free ways as possible or the route without using toll road, and the like. In this example, the navigation system displays a progress scale of the calculation of the route.
After determining the guided route, the navigation system starts the route guidance as shown in FIG. 1H to guide the user along the calculated route to the destination. Typically, the navigation system shows the intersection which is highlighted to show the next turn and a direction of the turn. Such route guidance by the navigation system is also accompanied by voice instructions.
One of the methods to specify the destination is to directly utilize POI icons on a map image an example of which is shown in FIGS. 2A-2E. Typically, in FIG. 1A, a mark for the vehicle current position (VP) is shown on the map image at the center of the screen. If the map image is in an appropriate map scale, POI icons 21-22 will be also displayed in the map image as shown in FIG. 2A. The user scrolls the map image and moves a region of attention close to the cursor 24 which is, for example, fixed at the center of the screen. Then, in FIG. 2B, a balloon message “POI Icon List” will be displayed which indicates that a list of POI in the area of the cursor 24 will be displayed in the next screen.
Thus, when the map image is zoomed-in as shown in FIG. 2C so that the POI may be easily identified, and the enter key is pressed, the navigation system displays a POI name list 25 as shown in FIG. 2D. If the user selects a preferred POI, for example, “Mobile” as a destination, then, the address of the POI 23 is displayed on the name list. By further pressing the enter key, a “Confirm Route” screen is displayed as shown in FIG. 2E. If the “OK to Proceed” key is pressed, the navigation system calculates the route and performs the route guidance to the destination.
As described above, the user can also specify the route to the destination by directly using the map image on the screen. However, the user may have difficulty in specifying the destination when searching the POI icons on the map image because sometimes too many POIs are located in a small area such as in a downtown, a shopping mall or other large compounds. Thus, when the user scrolls the map image of the downtown to display an region of attention, many POI icons 27 will be displayed such as shown in FIG. 3B.
In such a situation, although the user scrolls and moves the crowded POI icons around the center in the map images, he cannot easily identify the icons because some POI icons. 27 are overlapped. The problem becomes worse if there are many overlapping POI icons (for example, restaurants) crowded in such an area. Because each POI icon needs to have a sufficient size for a user can see it on the navigation screen, POI icons will be overlapped when many POI icons have to be displayed within in a small area. Further, because a monitor screen of a navigation system has a limited resolution, it is difficult to display POI icons with a small size while maintaining clear view for the user.
As described in the foregoing, it is not always possible to display POI icons and their positions on the map image due to the limitation of the screen resolution and POI icon sizes. As a result, it is not possible to decide as to which side of the street a particular POI is located. As noted above, frequently, POI icons are overlapped and the user cannot distinguish one POI icon from the other. Thus, it is not easy for the user to specify the destination by the method of directly using POI icons on the map image. Thus, there is a need for a new display method for easily and quickly distinguishing the POI icons.